Contributed Session II: High-resolution assessment of saccadic landing positions for S-cone-isolating targets.

The role of S-cone signals in guiding visuomotor behavior is not fully understood. Previously, we used high-resolution retinal tracking during a visual search-and-identification task to show that the preferred retinal locus (PRL) of fixation for S-cone-isolated targets was larger than and offset from the PRL measured with L/M-isolating optotypes (Wang et al, ARVO 2023). Here, we present an analysis of saccadic landing behavior under these conditions. We used an adaptive optics ophthalmoscope to record retinal videos while subjects (N = 6) made small saccades to a tumbling-E stimulus that appeared at random loci within a 3x3 square grid with 0.5° spacing. Subjects reported stimulus orientation via keypress, after which the target moved to a new location. Retinal videos recorded during each experiment were used to extract eye position traces and localize stimuli in retinal coordinates. Saccade PRLs were computed from the post-saccadic retinal landing positions using the ISOA method. The mean (± SEM) saccade PRL areas were 122 ± 8.1 arcmin2 and 525 ± 133 arcmin2 for the L/M- and S-cone conditions, respectively (p<0.01; Wilcoxon rank-sum test). For both conditions, the post-saccadic ISOA size reduced over the course of ~300 ms. The average displacement between the L/M- and S-cone saccade PRL was 7.72 ± 1.24 arcmin, similar to that reported previously for fixation, suggesting the retinal locus directed to a target of interest depends on the visual pathway mediating its detection.